1. Field of the Invention
The present invention relates to open-head power tongs used in drilling operations, and more particularly, is directed to an improved indexing mechanism for aligning the side opening of the frame with the side opening of the pipe engaging jaw mechanism to thereby facilitate removal of the tong from a drill string.
2. Description of the Prior Art
In drilling operations, several drill pipes are threadably connected together in a make-up operation to form a drill string, whereas, during a break-out operation, the pipes are disconnected from one another. In either making-up or breaking-out of a drill string, the general practice is to hold the lower pipe while the upper pipe is rotated. There are several different types of equipment on the market for performing each of these functions, one such device commonly used for rotating the upper pipe is an open-head power tong, such as the one shown and described in U.S. Pat. No. 4,060,014, whereas, another common piece of equipment used for holding the lower pipe is a back-up tong such as the one shown and described in U.S. Pat. No. 4,005,621.
The open-head power tong basically includes a bifurcated frame that defines a drill pipe receiving central opening and a side opening that communicates with the central opening for permitting a drill pipe to laterally pass therethrough. Housed within the frame is a rotatably supported pipe engaging and gripping mechanism that generally includes a ring or rotor having a side opening and which carries a plurality of jaws that move into and out of the central opening of the frame to thereby grip a pipe and rotate the same as the mechanism is driven in either a clockwise or counterclockwise direction during respective make-up and break-out operations.
After either a make-up or break-out operation has been terminated, generally the jaws of the engaging mechanism are still engaged on the pipe and normally the side opening of the rotor is not in alignment with the side opening in the frame; and therefore, before the tong can be removed from the drill string, the jaws first must be disengaged and the side openings aligned. To disengage the jaws and align the openings, it is necessary to rotate the engaging and gripping mechanism in a direction opposite to that of what it has been previously driven. Generally, this is accomplished by an operator changing the direction of the flow of fluid to the hydraulic motor and then normally squeezing the throttle valve to slowly rotate the engaging mechanism so as to achieve a proper alignment of the openings. This is a very time consuming task, especically with those tongs that produce high torques.
There has been different approaches to facilitate this alignment problem; however, each has its disadvantages. One such approach involves a complexed mechanical linkage arrangement so interconnected to the hydraulic drive motor to stop the flow of fluid to the motor, and thus, stoppage of the motor when a cam, prepositioned on the rotor, engages a portion of the linkage. With such an arrangement the operator must first change the rotational direction of the motor and then squeeze the throttle to start the rotation. Besides, not being fully automatic, such approach involves a complex linkage, and furthermore, does not work satisfactorily on all tongs, expecially those larger tongs that create high torque outputs.
A second approach to the alignment problem is shown in U.S. Pat. Nos. 3,261,241 and 3,180,186 wherein the alignment mechanism basically includes a sophisticated and expensive hydraulic circuit having various hydraulic components so interconnected and related to the hydraulic drive motor to actuate the motor in a reverse direction and stop the same upon engagement with a prepositioned cam on the rotor so as to properly align the side openings. Such second approach does not function completely automatically and furthermore, is expensive, yet alone being difficult to maintain and repair.